Don't get me wrong, Thunderbird is awesome for what it is (and the Mail thingy was kinda perfect as a lightweight mail client) but Thunderbird has some rough edges.
Like it took me long until I figured out how to show message size, filter by date and then sort it by message size. Of course, the Mail thingy wasn't able to do something like that, but I remember waaaaaaaaaaaaaay back, that Communicator (that Mail program which came with Netscape / Mozilla) was way simpler to use than Thunderbird. But maybe my memories are hazy as this was like ~15 - ~20 years ago.
I’ve been helping people to Thunderbird. Most people are like: Mail>Thunderbird>New Outlook thingy. Good enough for me ;)